Advanced video coders-decoders (CODECs), such as motion picture experts group (MPEG2) or H.264 advanced video coding (AVC), uses intra-coded and inter-coded predication to achieve a high compression rate. An inter-coded picture uses information from other pictures for compression. Therefore, the packet/frame loss in a compressed picture will not only degrade the quality of the picture itself, but also affect the quality of all pictures that use this picture as a reference for the inter-coded prediction. For example, a packet loss of an I frame could potentially have adverse effects on all pictures in that group of pictures (GOP).
In a commercial digital TV broadcast system, video data streams are sent from head-end streaming servers through a backbone network to a number of multicast switches, from which video data streams are multicast to multiple residential set-top boxes as shown in FIG. 1a. The data integrity in the backbone transport is of high importance. Any packet loss in the backbone transport will propagate to all the downstream set-top boxes as shown in FIG. 1b. 
In real-time streaming, user datagram protocol (UDP) is often used to transport streams. UDP by itself does not guarantee the quality of service. To offer high quality of commercial video services (e.g. 99.999% of the time without errors), the packet loss rate should be very low (less than 1×10E-6) in the backbone network, far less than the packet loss rate of 1×10E-3 defined in the class 0 network service (best) in ITU Y.1541. Forward error correction (FEC) or a selective re-transmission technique can significantly decrease the effective packet loss rate. But in a real system, packet loss could still occur for various reasons.
When packet loss does occur, it is important to reduce the subjective video artifacts presented to the end users. An error concealment technique is normally used for that purpose. Error concealment techniques utilize information from either temporal or spatial neighbors to conceal the errors in the corrupted regions or frames. However, error concealment generally does not have good performance when lost packets include reference frames (I or P) data or when a large number of consecutive frames are entirely lost.
Previous efforts have been made to reduce the packet loss rate in the multicast backbone network. FEC is a practical way to significantly increase the quality of service (QoS). Some recent studies have focused on improving FEC algorithms. However, strong FEC often demands high computation power and introduces significant additional latency in the video data stream transport, whereas weak FEC often does not have adequate performance for a prolonged outage (e.g. >2 seconds). Adaptive FEC uses two way communications to dynamically adjust the strength of the FEC, but the complexity of the system is much higher.
Some IPTV systems (e.g. maximum service television (MSTV)) use re-transmission to perform loss recovery. There are two types of multicast data loss recovery schemes, namely source-based and distributed recovery. The distributed multicast data loss recovery schemes usually outperform source-based video data loss recovery schemes in efficiency and recovery latency, both of which are essential for large-scale video multicast. But the distributed loss recovery schemes require active loss recovery components deployed at multiple nodes at different levels of the hierarchical network topology. The source-based recovery scheme is easier to implement and requires fewer active components in the network, but it is less efficient especially in a large scale deployment. Also, the server could be flooded by large number of re-transmission requests, namely the negative acknowledgment (NAK) implosion problem.
Some commercial systems that demand stringent QoS level use redundant paths for the backbone transport; one is used for the primary path and the other is used as a backup path. Such a system has very high reliability but the cost in terms of network transport is almost doubled.
The present invention addresses the above problems.